P2: USGS Topographic and USGS Large-Scale Aerial Imagery won't load?

Previously, I was able to use the layers titled "OSM US USGS Topographic Maps" and "OSM US USGS Large-Scale Aerial Imagery" as backgrounds in Potlatch 2. Although at times slow to load and despite the fact that some tiles wouldn't ever load (especially with the Topo maps), they were quite useful for streams (Topo maps) and building outlines (Large-scale aerials). That changed about three days ago. Now neither layer will load at any zoom level. Are these layers still available? Or is there some other reason for their unavailability?

I also noticed about the same time the backgrounds stopped working that the "M" shortcut ("Maximise Editor" mode) seems to glitch. The OpenStreetMap panel at the left of the screen goes away, but is replaced by a white box within the editing window. Pressing "M" a second time restores the OpenStreetMap panel, but leaves the white box. (This issue has been resolved.)

The missing background layers and the "M" glitch all recur when I relaunch the browser and/or restart the computer. The version (from the "Help" window) is given as: Version 2.3, Build 2.3-509-g0221790